This invention relates to a circuit arrangement for operating at least one high-pressure gas discharge lamp at a current of higher frequency, which comprises a full-wave rectifier for connection to an alternating voltage source and having direct voltage output terminals connected to a first circuit part comprising a switching transistor, a choke coil, a fly-wheel diode and a storage capacitor for feeding the lamp. The duty cycle and/or the switching frequency of the switching transistor are controlled by a control device in such a manner such that the current load on the alternating voltage source is as sinusoidal as possible.
The term "current of higher frequency" is to be understood herein to mean a current of a periodically varying value having a frequency between 1 kHz and 500 kHz and preferably between 20 kHz and 150 kHz.
Such a circuit arrangement comprising, for example, a boost or up converter as the first circuit part is known from EP OS No. 0059053. In general, storage capacitors in comparatively high capacitance are used, for example, 220 .mu.F/400 V with a power consumption of the lamp of 130 W. In order to guarantee a minimum life of the storage capacitors, a comparatively large number of electrolytic capacitors is required. Otherwise, the capacitors would be heated excessively due to the high-frequency current pulses. Therefore, it would be desirable to use foil capacitors for the storage capacitors. In the known circuit arrangements, however, this solution would have the disadvantage that due to their low storage capacity per unit volume, no constant direct voltage, but a direct voltage pulsating at double the mains frequency occurs at the storage capacitor. However, only a small direct voltage fluctuation is often desirable. The control for a usually employed boost or up converter is very simple if a constant output direct voltage is presupposed. On the other hand, not too large a voltage fluctuation is also favourable for the operation of high-pressure gas discharge lamps because these lamps extinguish at voltages below their operating voltage. The reignition of high-pressure gas discharge lamps is only possible, however, if shortly after the lamp has extinguished again a sufficient voltage (re-ignition voltage) is available at the storage capacitor.